Solvent dyeing of textile fibers and fabrics has become increasingly important in the industry's efforts to reduce waste discharged to our environment as well as increase productivity of the dyeing process. The more successful approaches to utilization of solvents to replace water in the dyeing processes suffer from the physico-chemical property differences between solvents and water, as, for example, high solubility of dyestuffs in the solvent resulting in poor dye yields, low distribution coefficients of solvent-soluble dyestuffs with fibers resulting in a poor distribution of dyestuff between the fiber and the solvent. These two properties alone make solvent dyeing unattractive for large volume uses.
Further, conventional aqueous dyeing techniques generate large quantities of waste material which previously had been dumped into streams creating ecological problems.
It therefore would be advantageous to have a process which could dye fibers, particularly polyester fibers, employing solvents which, in spite of the physico-chemical properties of the solvent-dye system, can obtain a substantial exhaustion of the dyestuff from the solvent.
The invention described herein permits the recycle of all of the fluids of solvent and water because less chemical additives are used than in the conventional dispersed dye system for polyester fibers. Additionally, the use of the solvent, with its inherent low latent heat of vaporization, permits distillation at locations where fuel costs are economical. The present invention also reduces the amount of fluids necessary for dyeing, thus permitting the use of means such as distillation, carbon adsorption, reverse osmosis, biodegradation, flocculation, filtration or combinations thereof as needed to purify and recycle substantially all of the fluids.